Re: 9.5 release notes - Mailing list pgsql-hackers

Hi,

On 2015-06-11 00:15:21 -0400, Bruce Momjian wrote:
> I have committed the first draft of the 9.5 release notes.  You can view
> the output here:

So, I did a pass through master's state:

>      <listitem>
>       <para>
>        Add <link linkend="BRIN">Block Range Indexes</> (<acronym>BRIN</>)
>        (Álvaro Herrera, Heikki Linnakangas, Emre Hasegeli)
>       </para>
>
>       <para>
>        <acronym>BRIN</> indexes are very compact and store the min/max
>        values for a range of heap blocks.
>       </para>
>      </listitem>

Maybe we should mention that they're cheap to maintain?

>      <listitem>
>       <para>
>        Improve in-memory hash performance (Tomas Vondra, Robert Haas)
>       </para>
>      </listitem>

"hash performance" is pretty general, there's lot of places where we use
hashing that aren't affected.

>      <listitem>
>       <para>
>        Improve concurrency of <link linkend="guc-shared-buffers">shared
>        buffer</> replacement (Robert Haas, Amit Kapila)
>       </para>
>      </listitem>

I think in the end that patch was enhanced to a significant degree by
making it lockless in d72731a70450b. I think the three (?) involved
patches should just combined under one entry.

>      <listitem>
>       <para>
>        Improve concurrent locking and buffer scan performance (Andres
>        Freund, Kevin Grittner)
>       </para>
>      </listitem>

If this is ab5194e6f, I don't think it makes sense to mention "buffer
scan" - it's just any lwlock, and buffer locks aren't the primary
benefit (ProcArrayLock, buffer mapping lock probably are that). I also
don't think Kevin was involved?

I think ed127002d8 and 4b4b680c should be mentioned in this section as
well. 4b4b680c will considerably reduce the per backend memory usage for
servers with large shared buffers.

>    <sect4>
>     <title>Server Settings</title>
>
>     <itemizedlist>
>
>      <listitem>
>       <para>
>        Replace <varname>checkpoint_segments</> with <link
>        linkend="guc-min-wal-size"><varname>min_wal_size</></> and
>        <link linkend="guc-max-wal-size"><varname>max_wal_size</></>
>        (Heikki Linnakangas)
>       </para>
>
>       <para>
>        This allows the allocation of a large number of <acronym>WAL</>
>        files without keeping them if they are not needed.
>       </para>
>      </listitem>

Hm. This affects performance significantly, should we also list it there?

>      <listitem>
>       <para>
>        Add <acronym>GUC</> <link
>        linkend="guc-wal-compression"><varname>wal_compression</></> to
>        enable compression of full page images stored in <acronym>WAL</>
>        (Rahila Syed, Michael Paquier)
>       </para>
>      </listitem>

Also rather performance relevant?

>      <listitem>
>       <para>
>        Archive <acronym>WAL</> files with suffix <literal>.partial</>
>        during standby promotion (Heikki Linnakangas)
>       </para>
>      </listitem>

This should be expanded, will mention to Heikki. Possibly also need to
be mentioned in the backward incompat section.

>      <listitem>
>       <para>
>        Allow the <link linkend="pg-replication-origin-create">labeling</>
>        of the origin of logical replication changes (Andres Freund)
>       </para>
>
>       <para>
>        This helps with change tracking.
>       </para>
>      </listitem>

I think it should be 'origin and progress'. The explanation should
probably rather be 'This is helpful when implementing replication
solutions" or something like it.


>      <listitem>
>       <para>
>        Allow control of table <acronym>WAL</> logging after table creation
>        with <link linkend="SQL-ALTERTABLE"><command>ALTER TABLE .. SET
>        LOGGED / UNLOGGED</></> (Fabrízio de Royes Mello)
>       </para>
>      </listitem>

This sounds a bit confusing. Maybe "Allow to convert a WAL logged table
to an UNLOGGED one, and the other way round"?


>    <sect4>
>     <title>System Information Functions and Views</title>

I wonder if

>      <listitem>
>       <para>
>        Report the backends holding replication slots in <link
>        linkend="catalog-pg-replication-slots"><structname>pg_replication_slots</></>
>        (Craig Ringer)
>       </para>
>
>       <para>
>        The new output column is <structname>active_pid</>.
>       </para>
>      </listitem>

shouldn't be moved her?

>      <listitem>
>       <para>
>        Allow <application>pg_dump</> to share a snapshot taken by another
>        session using <option>--snapshot</> (Simon Riggs, Michael Paquier)
>       </para>
>
>       <para>
>        The remote snapshot must have been exported by
>        <function>pg_export_snapshot()</> or been defined when creating
>        a logical replication slot.

'or exported by logical replication slot creation'?

>        This can be used by parallel
>        <application>pg_dump</> to use a consistent snapshot across
>        <application>pg_dump</> processes.
>       </para>

What do you mean by this comment? Parallel pg_dump internally does all
the snapshot stuff already, and it's independent of this option.

>      <listitem>
>       <para>
>        Change <application>pg_ctl</> default shutdown mode from
>        <literal>smart</> to <literal>fast</> (Bruce Momjian)
>       </para>
>      </listitem>

Wonder if this should be listed as an incompatibility. This does have
have impact on existing setups/scripts.

>      <listitem>
>       <para>
>        Add basic atomics <acronym>API</> support (Andres Freund, Oskari
>        Saarenmaa)
>       </para>
>      </listitem>

Out of fairness I think either Oskari shouldn't be listed, or Amit
should as well. Amit surely has spent more time on the patch than
Oskari.

>      <listitem>
>       <para>
>        Add native compiler and memory barriers for <productname>Solaris
>        Studio</> (Oskari Saarenmaa)
>       </para>
>
>       <para>
>        IS THIS PART OF ATOMICS?
>       </para>
>      </listitem>

Not really, barriers are independent. But I guess we could just combine
it nonetheless.

>   <sect3>
>    <title>Additional Modules</title>
>
>    <itemizedlist>
>
>     <listitem>
>      <para>
>       Add <link linkend="app-pgrewind"><application>pg_rewind</></>,
>       which allows re-synchronizing a master server after failback
>       (Heikki Linnakangas)
>      </para>
>     </listitem>

Hm. pg_rewind isn't in contrib, so is this the right place for this?


I think 647248e3708, 4fe384bd85, 4f85fde8, 59f71a0d0 should also be
mentioned. They're amongst the most invasive changes in 9.5, and they do
have implications for developers and users.

f5ae3ba4/779fdcd should be listed as improving bitmap index scan
performance.

Greetings,

Andres Freund